Ethanol treatment triggers a heat shock-like response but no thermotolerance in soybean (Glycine max cv. Kaohsiung No.8) seedlings

Abstract

Non-lethal heat-shock (HS) treatment has previously been shown to induce thermotolerance in soybean (Glycine max cv. Kaohsiung No.8) seedlings. This acquired thermotolerance correlates with the de novo synthesis of heat-shock proteins (HSPs). Interestingly, we found that ethanol treatments also elicited HS-like responses in aetiolated soybean seedlings at their normal growth temperature of 28 °C. Northern blot analyses revealed that the expression of HS genes hsp17.5, hsp70 and hsc 70 was induced by ethanol. Radioactive amino acids were preferentially incorporated into high molecular weight (HMW) HSPs rather than class I low molecular weight (LMW) HSPs during non-lethal ethanol treatments. Immunoblot analysis confirmed that no accumulation of class I LMW HSPs occurred after non-lethal ethanol treatment. Pre-treatment with a non-lethal dose of ethanol did not provide thermotolerance, as the aetiolated soybean seedlings could not survive a subsequent heat shock of 45 °C for 2 h. In contrast, non-lethal HS pre-treatment, 40 °C for 2 h, conferred tolerance on aetiolated soybean seedlings to otherwise lethal treatments of 7.5% ethanol for 8 h or 10% ethanol for 4 h. These results suggest that plant class I LMW HSPs may play important roles in providing both thermotolerance and ethanol tolerance.